Various ultrasound techniques and devices have been developed for imaging the interior of a body e.g. the human body. One application of ultrasound imaging has been in the medical field, and in particular, in endocavitary probes (e.g., biopsy guidance endocavitary probes). Such probes may be used, for example, for endovaginal examination (e.g., to examine the uterus, ovaries, etc.), endorectal examination (e.g., to examine the rectal wall, prostate, etc.), and/or other medically-related applications. It should be noted that for instance endorectal examination is rather unpleasant and that biopsy taking is rather painful and therefore typically requires local anaesthesia. Typically, endocavitary probes include a linear array transducer positioned at the distal end or front end of the probe that is to be inserted into a cavity of a body. The transducer provides an imaging plane for viewing structures/features of the body and/or another instrument (e.g., a biopsy needle) that, for example, may be guided into the body via the probe. The imaging plane may be provided at a side of a probe (corresponding to a “side-fire” transducer) or the front of the probe (corresponding to an “end-fire” transducer).
Endocavitary probes typically have an elongated rod-like shape configured with a handle that extends as a portion of the elongated rod-like shape, but in the end opposite the distal end. Other ultrasound probes are, contrary to endocavitary probes, configured for placing the probe on the skin of the body to provide imaging of the interior of the body located beneath the skin. Still other probes (e.g. intra-operative probes) are configured for placing the probe directly on organs inside the body during surgery operations.
Ultrasound probes are, during use as a probe for imaging purposes, connected to an image processor e.g. in the form of a special purpose computer. The image processor is configured to provide stimulation signals to the probe for emission of ultrasound pulses and to record reflected ultrasound signals in response thereto. Recorded ultrasound signals are processed to provide a presentation of the reflected ultrasound signals in the form of an ultrasound image on a display screen e.g. a computer monitor.
Use of an ultrasound probe for imaging purposes is also denoted ultrasound scanning or simply scanning. Scanning is commonly understood as the act of systematically emitting a (finely focused) beam of e.g. ultrasound into a medium at different locations across the medium in order to produce an image of structures contained in the medium. The beams are emitted systematically e.g. by transducer elements arranged in a linear or curved linear transducer array. An image is generated from reflections received in response to emitted ultrasound beams.
The transducer(s) of the probe has/have a so-called field of view which is the sector (usually with a shape like a sector of a circle) from which reflections are recorded and displayed as an image. The field of view is also denoted the imaging plane since field of view can be thought of as a very thin sector of a disc. A very thin sector is desired in order to provide precise spatial location (e.g. of organs or tumours). This is provided by focusing the emitted ultrasound waves in a direction transverse to the linear array. Thus, the sector can be described as a plane or sector of a circle, but it will have a certain thickness. The width of the field of view is determined by the length of the linear array and the shape of the array. Typically, the array is shaped to extend along an arc or a circle. The depth of the field of view is among other things determined by the length of a time-window within which reflected ultrasound signals are recorded.
The focusing required to obtain the desired field of view in a direction transverse to the length of the array is typically obtained by giving each of the transducer elements a concave surface shape (in a direction transverse to the length of the array). It is also desired to have a fine focusing in the image plane i.e. in a direction along the length of the array. This is typically achieved by giving each of the transducer elements a flat surface shape (in a direction transverse to the length of the array) and then obtaining a desired focusing electronically. The focused image acquired from the field of view comprises a number of radial lines. The number of radial lines in the image corresponds to radial scan lines (in the tissue scanned) along which focusing is provided. Thus, the field of view comprises a number of scan lines.
The probe typically provides either signals from a single transducer array for display as one image or rather sequence of images representing the ultrasound imaging from the field of view of the single transducer array. Some ultrasound probes comprise two arrays arranged perpendicular to each other to provide bi-plane imaging that is two separate images acquired from the two different arrays. Thereby a so-called sagittal image plane and transverse image plane can be provided for simultaneous display. Bi-plane imaging provides more spatial information due to acquisition of two images from two transducers with different fields of view.
For the vast majority of uses of endocavitary probes, the probe is used to monitor the safe guidance of an instrument e.g. a biopsy needle. This monitoring is typically carried out by means of a probe configured with a guide that guides the instrument along a predefined path. The transducer(s) of the probe and the guide are mutually arranged so as to remain in a fixed position relative to each other and so as to obtain a field of view which covers at least a portion of the predefined path along which the instrument is guided. Thereby safe guidance of an instrument can be obtained.
The above described observations and techniques are well-known in the field of ultrasound probes. Below, reference is made to different endocavitary probes.